Vertical structure schottky diode optical detector

Abstract

A vertical structure Schottky contact photodiode has a narrow bandgap InGaAs light absorbing layer cladded front and back with InAlAs current blocking layers having metal contacts formed thereon. As compared to single-side MSM photodiodes, with interdigitated electrodes lying in a single plane, response time is improved due to reduced spacing between the electrodes. Response time is also improved since capacitance is reduced due to inherently low doping levels in the semiconductor material. Laterally offset finger electrodes are made light reflective to increase the production of carriers in the InGaAs absorption layer.

What is claimed is: 
     
       1. A vertical metal-semiconductor-metal photodetector comprising: (a) an InGaAs optical absorbing layer having a first InAlAs current blocking layer positioned over said InGaAs optical absorbing layer, and a first electrode means including a first set of metallic electrodes positioned over said first current blocking layer and in contact therewith, said first set of electrodes having light transmissive areas between said metallic electrodes; and   (b) a second InAlAs current blocking layer positioned under said optical absorbing layer, and second electrode means in contact with an underside portion of said second InAlAs current blocking layer.   
     
     
       2. The photodetector of claim 1 wherein said InGaAs optical absorbing layer has a thickness of 0.2-1.0 micrometers, and said InAlAs blocking layers each have thicknesses of between 25-100 nanometers. 
     
     
       3. The photodetector of claim 1 wherein said first set of metallic electrodes comprise elongated fingers. 
     
     
       4. The photodetector of claim 2 wherein said first set of metallic electrodes comprise elongated fingers. 
     
     
       5. The photodetector of claim 3 wherein said second electrode means includes a second set of fingers, laterally offset with respect to the first set of fingers of said first electrode means, for increasing the light absorption ability of said optical absorbing layer. 
     
     
       6. The photodetector of claim 4 wherein said second electrode means includes a second set of fingers, laterally offset with respect to the first set of fingers of said first electrode means, for increasing the light absorption ability of said optical absorbing layer. 
     
     
       7. The photodetector of claim 1 wherein semiconductive light reflective means is positioned upon a lower portion of the photodetector for directing light coming from an upper portion of the photodetector back through the optical absorbing layer for increasing the light absorption ability of said optical absorbing layer. 
     
     
       8. The photodetector of claim 2 wherein semiconductive light reflective means is positioned upon a lower portion of the photodetector for directing light coming from an upper portion of the photodetector back through the optical absorbing layer for increasing the light absorbtion ability of said optical absorbing layer. 
     
     
       9. The photodetector of claim 5 wherein semiconductive light reflective means is positioned upon a lower portion of the photodetector for directing light coming from an upper portion of the photodetector back through the optical absorbing layer for increasing the light absorption ability of said optical absorbing layer. 
     
     
       10. The photodetector of claim 6 wherein semiconductive light reflective means is positioned upon a lower portion of the photodetector for directing light coming from an upper portion of the photodetector back through the optical absorbing layer for increasing the light absorption ability of said optical absorbing layer. 
     
     
       11. The photodetector of claim 1 wherein said second electrode means includes a light reflective Schottky barrier layer. 
     
     
       12. The photodetector of claim 7 wherein said second electrode means includes a light reflective Schottky barrier layer. 
     
     
       13. The photodetector of claim 8 wherein said second electrode means includes a light reflective Schottky barrier layer. 
     
     
       14. The photodetector of claim 9 wherein said second electrode means includes a light reflective Schottky barrier layer. 
     
     
       15. The photodetector of claim 10 wherein said second electrode means includes a light reflective Schottky barrier layer. 
     
     
       16. A vertical metal-semiconductor-metal photodetector comprising: (a) an InGaAs optical absorbing layer having a first InAlAs current blocking layer positioned over said InGaAs optical absorbing layer, and a first electrode means positioned over said first current blocking layer and in contact therewith; and   (b) a second InAlAs current blocking layer positioned under said optical absorbing layer, and second electrode means in contact with an underside portion of said second InAlAs current blocking layer.   
     
     
       17. The photodetector of claim 16 wherein said InGaAs optical absorbing layer has a thickness of 0.2-1.0 micrometers, and said InAlAs blocking layers each have thicknesses of between 25-100 nanometers. 
     
     
       18. The photodetector of claim 16 wherein light reflective means is positioned upon a lower portion of the photodetector for directing light coming from an upper portion of the photodetector back through the optical absorbing layer for increasing the light absorption ability of said optical absorbing layer. 
     
     
       19. The photodetector of claim 1 wherein said InAlAs current blocking layers are undoped. 
     
     
       20. The photodetector of claim 2 wherein said InAlAs current blocking layers are undoped. 
     
     
       21. The photodetector of claim 16 wherein said InAlAs current blocking layers are undoped. 
     
     
       22. The photodetector of claim 17 wherein said InAlAs current blocking layers are undoped.